1. Field of the Invention
The present invention is directed in general to semiconductor devices and methods for manufacturing same. In one aspect, the present invention relates to wire ball bonding and associated methods of fabricating and testing same.
2. Description of the Related Art
Ball bonding is widely employed in the semiconductor packaging industry to form electrical connections between an integrated circuit die and a die carrier such as a lead frame or a substrate. Conventional ball bonding processes use a combination of heat, pressure and ultrasonic energy to form an intermetallic connection or weld between a wire and a connection pad, typically forming a u-shaped bond interface with the thinnest portion of the connection pad being centrally located under the wirebond. However, the connection pad is typically subjected to a number of stressors such as temperature cycling, impact force, contact power, contact force, bond power and bond force during the ball bonding process, leading to mechanical integrity problems, such as cracks between the connection pad and bonding ball that can form during bonding, device operation or device testing, such as highly accelerated stress test (HAST). For example, accumulated stress due to coefficient of thermal expansion (CTE) mismatch in temperature cycling situations can exceed the aluminum strength, causing aluminum fatigue and aluminum cracking underneath copper ball bonds. While such stress effects are mitigated somewhat with conventional copper ball bonds formed with large ball bond structures (e.g., wire diameters larger than 50 microns and ball diameters larger than 100 microns) formed on high-k dielectric layers in short interconnect stacks (e.g., 1-2 BEOL interconnect levels) without active circuits located beneath the bond structure, such conventional copper ball bond structures are extremely difficult at a practical level to use with state of the art devices.
It will be appreciated that for simplicity and clarity of illustration, elements illustrated in the drawings have not necessarily been drawn to scale. For example, the dimensions of some of the elements are exaggerated relative to other elements for purposes of promoting and improving clarity and understanding. Further, where considered appropriate, reference numerals have been repeated among the drawings to represent corresponding or analogous elements.